Drilling unit, method for slot drilling and slotting device

ABSTRACT

A slotting device ( 100 ) to be used with a rock drilling apparatus ( 1 ) to drill closely together a plurality of parallel intersecting holes so as to form a slot in a brittle material, such as rock, masonry or concrete. The slotting device ( 100 ) includes a guide portion ( 110 ) connected to a body portion ( 120 ) with at least one strut ( 130 ). The guide portion ( 110 ) is disposed in a previously drilled hole, and the body portion ( 120 ) and a rotary percussion tool ( 7 ) mutually define a variable volume chamber ( 140 ) that contains flushing fluid that damps transmission of impact stress waves from a percussion device ( 4 ) of the drilling apparatus ( 1 ) to the slotting device ( 100 ).

FIELD OF THE INVENTION

The present invention relates to a drilling unit and method for slotdrilling and a slotting device. In the slot drilling a plurality ofholes are drilled closely together so as to form a slot in a rockmaterial. A slot may be formed in a rock surface or into rock mass bydrilling a plurality of holes in the surface at a pitch substantiallyequal to the diameter of the holes. In the slot drilling a specialslotting device is needed for guiding the drilling tool along apreviously drilled hole. The object of the invention is disclosed moreclosely in the preambles of the independent claims.

BACKGROUND OF THE INVENTION

Slot drilling is a method used in underground and surface mining. In theslot drilling holes are successively drilled very close to each otherand when a new hole is drilled next to a previously drilled hole, thewall of rock between the holes is broken. In this manner, a continuousslot is formed by the holes as they are successively drilled. Suchcontinuous slots i.e. elongated voids can be used in the surfaceblasting to protect buildings near a blasting site. In this mannerpropagation of the shock waves outside the blasting site is prevented.In the underground mining elongated voids or slots can be drilled insolid rock for example in a tunnel face in order to form a primary openspace whereto a broken rock material can expand in blasting. This isneeded e.g. in stope opening or drifting.

When a single hole is drilled into rock, the fully circumferential wallof the hole remains intact and radial forces acting from the wall of thehole on the drill bit tend to cancel each other. However, in the slotdrilling, when a plurality of holes are formed in a row so as to form aslot, the wall of rock between a previously drilled hole and a new holebeing drilled is broken as the new hole is being drilled, and the radialforces acting from the partially circumferential wall of the new hole onthe drill bit result in a net force that is directed toward thepreviously drilled hole.

Therefore, the drill bit as it drills the new hole tends to be displacedradially off a desired course under the combination of radial forcesthus applied. To prevent the drill bit from being displaced, it has beena conventional practice to use a guide rod supported parallel to thedrill rod and having a diameter, which is substantially the same as orslightly smaller than the diameter of holes to be formed. Before a newhole is drilled, the guide rod is inserted into a previously drilledhole next to the position of the new hole so as to stabilize the supportfor the drill rod. By placing the guide rod in the previously drilledhole, the support for the drill rod is prevented from shifting positioneven when large radial forces are imposed on the drill rod as it drillsthe new hole.

U.S. Pat. No. 5,690,184 discloses a rock drilling unit for slotdrilling. The drilling unit includes a guide rod fixed to a support forthe drill rod at the front end of the feeding beam, whereby the guiderod extends to the front of the feeding beam. Thus, the drilling unit isdesigned only for slot drilling.

WO 99/45 237 discloses a slotting device, which includes a down-holerock drilling machine inside a body portion of the slotting device and aparallel guide tube arranged by means of a strut to the body portion.One disadvantage of the disclosed slotting device is that stress wavesgenerated by a percussion device of the drilling machine are transmittednot only to a tool but also to the body structure and to the guide tube.The stress waves may cause serious damages to the body and the guide ofthe slotting device. This said disadvantage concerns especially tophammer applications.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is to provide a new and improved drillingunit and method for slot drilling and further a new and improvedslotting device.

The drilling unit of the invention is characterized in that between thebody portion of the slotting device and the tool there is at lest oneaxial volume chamber containing fluid so as to dampen transmission ofthe impact stress waves from the percussion device to the slottingdevice.

The slotting device of the invention is characterized in that theslotting device is provided with at least one axial volume chamberbetween the body portion and the tool; and wherein the slotting devicecomprises at least one flow channel for directing fluid into thechamber, whereby the fluid in the chamber is arranged to transmit axialforces from the tool to the body portion.

The method of the invention is characterized in that it comprises thesteps of transmitting the feed force to the body of the slotting devicein the drilling direction by means of fluid in at lest one axial volumechamber between the tool and the body portion; and dampeningtransmission of the impact stress waves from the percussion device tothe slotting device by means of the fluid in the at least one axialvolume chamber.

According to the present invention the slotting device comprises anaxial volume chamber that contains flushing fluid so as to dampentransmission of the impact stress waves from a percussion device to theslotting device. Accordingly, impact stress waves are transmitted to atool, but their transmission to a slotting device attached to the toolis damped. Further, during drilling feed force in the drilling directionis transmitted to the body of the slotting device by means of fluid.

An advantage of the invention is that in normal drilling situation thereis an axial gap in drilling direction between the mechanical countersurfaces of the tool and the body of the slotting device, whereby theenergy of the stress waves generated by a percussion device are nottransmitted to the body and to the guide of the slotting device. Thanksto this, stress waves do not damage the structure of the slotting deviceand the operating life of the slotting device may longer.

It is the idea of an embodiment that the slotting device is adismountable auxiliary device connected to a shank of the rock drillingmachine or to a drill rod connected to the shank. This being so, theslotting device can be easily connected and disconnected to a standardrock drilling machine according to the need. When the slotting device isdisconnected, the rock drilling machine can be used in drilling normalsingle holes.

It is the idea of an embodiment that fluid is provided to flush drillingwaste from a hole being drilled. Preferably, the fluid flows through anaxial volume chamber that is defined between a body portion of aslotting device and the tool, and the flushing fluid damps transmissionto the slotting device of impact stress waves generated by a percussiondevice.

It is the idea of an embodiment that the slotting device is capable ofdislodging itself in the event the slotting device becomes jammed in theslot.

It is the idea of an embodiment that the slotting device provides valvemeans regulating a flow of fluid through the axial volume chamber. Thevalve means restricts the fluid flow thereby increasing fluid pressureand providing additional force to move the slotting device if it becomesjammed.

It is the idea of an embodiment that the guide portion comprises a tubethat is spaced from and parallel to the body portion. Further the tubemay comprise a cutout in which an edge of the bit may rotate. Thiseliminates the risk that the drill bit comes in contact with the tube.

It is the idea of an embodiment that the guide portion comprises atleast one elongated guiding flange extending longitudinally along aperipheral surface of the guide portion. These elongated guide flangesensure that the distance of the hole being drilled is correct inrelation to the previous hole.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail bymeans of exemplary embodiments with reference to the attached drawings,in which

FIG. 1 a is a schematic illustration of a rock drilling rig;

FIG. 1 b is a schematic illustration of a rock drilling unit;

FIGS. 2 a-2 c are schematic illustrations showing how a slot is formedby successively drilling closely together a plurality of holes;

FIG. 3 is a first perspective view of a first embodiment of a slottingdevice according to the present invention;

FIG. 4 is a plan view of the slotting device shown in FIG. 3;

FIG. 5 is a partial cross-section view of the slotting device shown inFIG. 3;

FIG. 6 is a partial cross-section detail view of an area indicated inFIG. 5 and showing a first condition of the slotting device shown inFIG. 3;

FIG. 7 is a partial cross-section detail view similar to FIG. 6 butshowing a second condition of the slotting device shown in FIG. 3;

FIG. 8 is a second perspective view of the slotting device shown in FIG.3;

FIG. 9 is a schematic illustration showing a second embodiment of aslotting device according to the present invention;

FIG. 10 is cross-section view taken along line X-X in FIG. 9;

FIG. 11 is a cross-section view taken along line XI-XI in FIG. 10; and

FIG. 12 is a schematic illustration of a hold device through which theslotting device can be pushed.

In the Figures, some embodiments are shown in a simplified manner forthe sake of clarity. In the Figures, like parts are denoted with likereference numerals.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 a is a schematic illustration of a rock drilling rig 1, thatincludes a boom 2, at the end of which there is a rock drilling unit 60.The rock drilling unit 60, which is shown more detailed in FIG. 1 b,comprises a feed beam 3 with a rock drilling machine 6 including apercussion device 4 and possibly a rotating device 5. In general, thepercussion device 4 comprises a percussion piston that is operated by apressure medium, and strikes the upper end of a tool 7 or a connectingpiece arranged between the tool 7 and the percussion device 4, such as adrill shank 61. Naturally, it is possible to generate impact pulses inthe percussion device 4 in some other manner, for example electricallyor without a reciprocating striking piston. The proximal end of the tool7 is connected to the rock drilling machine 6 by means of the shank 61,and at the distal end of the tool 7 there is a fixed or detachable bit 8for breaking rock. Typically, the bit 8 is a drill bit with buttons 8 a,but other bit structures are also possible. The rotating device 5 maytransmit to the tool 7 continuous rotating force to cause the bit 8connected to the tool 7 to change its position after an impact of thepercussion device 4 and with a subsequent impact strikes a new spot inthe rock. The rock drilling machine 6 is arranged movably on the feedbeam 3 in drilling direction D and in reverse direction R and duringdrilling the tool 7 is thrust with a feeding device 9 against the rock62. The feeding device 9 can be for example a pressure-medium-operatedcylinder. When deep holes are drilled, i.e. in so-called extension roddrilling, drill rods 10 a, 10 b, 10 c (the number of which depends onthe depth of the hole to be drilled and which constitute the tool 7) arearranged between the bit 8 and the drilling machine 6. The drillingmachine 6 may comprise a flushing device 11 for supplying a flushingfluid through the tool 7 and the bit 8 to a bored drill hole so as toflush loose drilling waste there from. For the sake of clarity, FIG. 1 adoes not show the flushing channels of the tool 7. The rock drilling rig1 may also be provided with at least one control unit 63 for controllingthe drilling. Further, at the outermost end section of the feed beam 3there may be a holding device 64 through which the tool 7 is arranged.The hold 64 includes means for supporting the tool 7 during drilling.There may be also a drilling component magazine 65 for storing drillingcomponents such as drill bits 8, slotting devices and drilling rods 10.The component magazine 65 may be provided with a manipulator fortransferring drilling components between the drilling axis and themagazine. Thereby drilling components, such as the slotting device, canbe connected and disconnected to the drilling machine according to theneed.

Referring more particularly to FIG. 1 b, a feed pump 12 drives thefeeding device 9, an impact pump 13 drives the percussion device 4, anda rotation pump 14 drives the rotating device 5. The pumps 12, 13, 14supply pressurized fluid, preferably hydraulic oil, to the respectivededicated devices 9, 4, 5 that they drive. The pumps 12, 13, 14 aredisposed along supply conduits 15, 16, 17 respectively connected to thedevices 9, 4, 5 and through which pressurized fluid is supplied to thedevices in the direction indicated by arrows A. Alternatively the neededpressure fluid is supplied from one single pump to the devices. Thefluid is returned from the devices 9, 4, 5 along respective returnconduits 18, 19, 20 in the direction indicated by arrows B back to atank. The drilling machine 6 also comprises a flushing pump 21 that isdisposed along a supply conduit 22 that is connected to the flushingdevice 11. A flushing agent, which is typically water, is supplied tothe flushing device 11 in the direction of arrow A.

The feed pump 12, impact pump 13, rotation pump 14 and flushing pump 21are typically driven by motors 12 a, 13 a, 14 a, 21 a, respectively. Forthe sake of clarity, FIG. 1 b does not show control valves used for thecontrol of the devices 4, 5, 9 and 11. The structure and operation ofthe rock drilling rig 1 and machine 6 are known per se to the personskilled in the art, and therefore they are not discussed here in greaterdetail.

Referring now to FIGS. 2 a-2 c, a slot S is formed in a rock surface bydrilling a plurality of holes at a pitch substantially equal to thediameter of the holes. Since the holes are successively drilled veryclosely to each other, when a new hole is drilled next to a previouslydrilled hole, the wall of rock between these holes is broken. In thismanner, a slot is formed along the holes as they are successivelydrilled.

As shown in FIG. 2 a, when a single hole 50 is drilled in a rocksurface, the fully circumferential wall 50 a of the hole 50 is leftintact. The radial forces F (four of which are shown in FIG. 2 a) actingfrom the wall 50 a on the drill bit cancel each other, and the sum ofthe radial forces F is negligible. However, as shown in FIG. 2 b, when anew hole 52 is drilled adjacent to the previously drilled hole 50 so asto form a slot, a partition 51 of rock between the previously drilledhole 50 and the hole 52 being drilled is broken (this is indicated witha broken line in FIG. 2 b). Consequently, the broken partition 51 doesnot provide a radial force −F, and the sum of radial forces F acting onthe drill bit do not cancel each other. Instead, there is a resultantforce directed toward the previously drilled hole 50 and, as the newhole 52 is drilled, the drill bit tends to be displaced radially offfrom its desired course, i.e., parallel and intersecting the previouslydrilled hole 50.

Referring now to FIG. 2 c, the utilization of a slotting device 100according to the present invention will be described. The hole 50 isinitially drilled with a normal drill bit. Thereafter, the slottingdevice 100 is fitted to the rock drilling machine 6, and the holes 52and 54 are successively drilled. When hole 52 is being drilled, it isparallel to and intersects previously drilled hole 50, and when hole 54is being drilled, it is parallel to and intersects previously drilledhole 52. After completing hole 54, the tool 7 including the bit 8 iswithdrawn and positioned such that a guide portion 110 of the slottingdevice 100 will extend into the previously drilled hole 54. A bodyportion 120 of the slotting device 100, which is fitted with respect tothe tool 7 and connected to the guide portion 100 by at least one strut130, maintains the desired course for the new hole being drilled.

The guide portion 110 may be provided with one or more longitudinallyextending elongated guiding flanges 112 a, 112 b. Preferably, theguiding flanges 112 a, 112 b are disposed on the peripheral surface ofthe guide portion and are positioned on either side of the brokenpartition between the two previously drilled holes 52, 54. The guidingflanges 112 a, 112 b facilitate locating the guide portion 110 in thepreviously drilled hole 54, particularly with regard to the absence thatresults from the broken partition. Alternatively, a single flange thatextends on the peripheral surface of the guide portion 110 beyond theopposite ends of the broken partition may also facilitate locating theguide portion 110 in the previously drilled hole.

Referring now to FIGS. 3-8, a first preferred embodiment of the slottingdevice 100 are described in detail. Preferably, the guide portion 110,which is to be disposed in a previously drilled hole, is tubular andextends longitudinally between a tapered leading edge 114 and a trailingend 116, which may also be tapered to facilitate extraction of the guideportion from the previously drilled hole. A cutout 118 may be providedso as to avoid contact between the guide portion 110 and the bit 8 as itworks in the hole being drilled. As was previously described, theguiding flanges 112 a, 112 b may be disposed on the peripheral surfaceof the guide portion 110.

The slotting device 100 comprises one or more struts 130 for connectingthe guide portion 110 to the body portion 120. The strut 130 provide astructural link to convey movement of the body portion 120 to the guideportion 110, i.e., the guide portion 110 is displaced in the previouslydrilled hole in response to movement of the body portion 120. Thus, theconnection between the guide portion 110 of the slotting device 100 andthe rock drilling apparatus 1 is, preferably, solely via the strut 130and the body portion 120 of the slotting device 100.

The body portion 120 of the slotting device 100 is disposed in the holebeing drilled, and is coupled to the tool 7 via a mutually defined axialvolume chamber 140 that contains flushing fluid to damp transmission ofthe impact stress waves from the percussion device 4 to the slottingdevice 100.

The body portion 120 includes a sleeve 122 that defines a bore 124 inwhich extends the tool 7. The bore 124 includes a first diameter portion124 a, a second diameter portion 124 b that is smaller than the firstdiameter portion 124 a, a shoulder portion 124 c that extends betweenand couples the first and second diameter portions 124 a, 124 b, and athird diameter portion 124 d that is smaller than the second diameterportion 124 b. The portion of the tool 7 that extends through the bore124 includes a piston portion 7 a and a rod portion 7 b, which isproximal to the bit 8. Preferably, the piston and rod portions 7 a, 7 bare mechanically coupled between the drill rods 10 a, 10 b, 10 c, ifany, and the bit 8; but may alternatively be integrally formed as partof the tool 7. Thus, the impact stress waves generated by the percussiondevice 4 are transmitted via a direct mechanical coupling, i.e., via thetool 7 including the piston and rod portions 7 a, 7 b, to the bit 8.

The first diameter portion 124 a of the bore 124 slidingly receives thepiston portion 7 a of the tool 7, and the second diameter portion 124 bof the bore receives the rod portion 7 b of the tool 7. Thus, thevariable axial volume chamber 140 has an annular shape that is definedradially between the first diameter portion 124 a of the bore 124 andthe rod portion 7 b of the tool 7, and is defined axially between thepiston portion 7 a of the tool 7 and the shoulder portion 124 c of thebore 124. Preferably, flushing fluid is prevented from flowing betweenfirst diameter portion 124 a and the piston portion 7 a, such as with aseal 126.

The variable volume chamber 140 may contain flushing fluid, which issupplied via a flow passage 142 that connects a first internalpassageway 144 that extends through the tool 7 and a second internalpassageway 146 that also extends through the tool 7. With respect to thebit 8, the first internal passageway 144 is distally disposed, and thesecond internal passageway 146 is proximally disposed. Preferably, thesecond internal passageway 146 provides flushing fluid flow to the bit8. The flow passage 142 includes an axial flow passage 142 a, a firstgenerally radial flow passage 142 b, and a second generally radial flowpassage 142 c. The axial flow passage 142 a is disposed radially betweenthe rod portion 7 b of the tool 7 and the second diameter portion 124 bof the bore 124. The first generally radial flow passage 142 b connectsthe first internal passageway 144 of the tool 7 to a first axial end ofthe axial flow passage 142 a, and a second generally radial flow passage142 c connects a second axial end of the axial flow passage 142 a to thesecond internal passageway 146 of the tool 7. The first and secondgenerally radial flow passages 142 b, 142 c may extend obliquely orperpendicularly with respect to the axial flow passage 142 a and to thefirst and second internal passageways 144, 146.

The third diameter portion 124 d of the bore 124 in the sleeve 122slidingly receives the rod portion 7 b of the tool 7. Preferably,flushing fluid is prevented from flowing between third diameter portion124 d and the rod portion 7 b, such as with a seal.

In FIG. 6 is shown a first relationship between the body portion 120 ofthe slotting device 100 and the tool 7. Flushing fluid is supplied tothe variable volume chamber 140 via the first generally radial flowpassage 142 b. The flushing fluid contained in the variable volumechamber 140 serves to damp transmission to the slotting device 100 ofimpact stress waves generated by the percussion device 4 of the rockdrilling apparatus 1. Specifically, the impact stress waves generated bythe percussion device 4 are transmitted through the tool 7, but theslotting device 100 is generally isolated from the impact stress wavesby virtue of the coupling via the flushing fluid contained in the axialvolume chamber 140. Because of the fluid in the axial volume chamber 140there is a gap G between the pressure surfaces 70 and 71, whereby thereis no mechanical axial contact between the tool 7 and the sleeve 122.Additional flushing fluid continues to flow from the first internalpassageway 144, via the first generally radial flow passage 142 b, theaxial flow passage 142 a and the second generally radial flow passage142 c, to the second internal passageway 146, through the bit 8 and intothe hole being drilled.

The slotting device 100 is advanced, i.e., the guide portion 110 isdisplaced in the previously drilled hole and the body portion 120 isdisplaced along with the tool 7, in accordance with the operation of thefeeding device 9 and the flow of the flushing fluid along the tool 7that fills the axial volume chamber 140. The flushing fluid in the axialvolume chamber 140 affects on the first and second working pressuressurfaces 70 and 72 generating a force in drilling direction D andfurther on a third working pressure surface 71 generating a force inreverse direction R. Thus the fluid transfers the force that is suppliedfrom the feeding device 9, via the piston portion 7 a of the tool 7, tothe sleeve 122 of the body portion 120, via the working pressuresurfaces 70, 72, and on to the guide portion 110 via the strut 130. Butthe flushing fluid contained in the axial volume chamber 140 dampstransmission to the slotting device 100 of impact stress waves generatedby the percussion device 4 of the rock drilling apparatus 1.

In FIG. 7 is shown a second relationship between the body portion 120 ofthe slotting device 100 and the tool 7. In the event that the slottingdevice 100 becomes jammed, e.g., the guide portion 110 becomes stuck inthe previously drilled hole, a second relationship develops. Resistanceto the slotting device 100 advancing, in combination with the operationof the feeding device 9, causes flushing fluid flow through the axialflow passage 142 a to be restricted by virtue of the third diameterportion 124 d at least partially closing the second generally radialflow passage 142 c. This raises fluid pressure in the axial volumechamber 140, and thus increases the force acting to dislodge theslotting device 100. At the extreme of the second relationship, thesecond generally radial flow passage 142 c is completely closed and theflow of flushing fluid is blocked, which can be detected by the controlunit 63 or the operator of the rock drilling rig 1, and the tool 7 andslotting device 100 can be extracted from their respective holes.

Preferably, the first generally radial flow passage 142 b feeds into thevariable volume chamber 140 during the first relationship between thebody portion 120 of the slotting device 100 and the tool 7 of the rockdrilling apparatus 1. As the piston portion 7 a of the tool 7 isdisplaced relative to the sleeve 122 of the body portion 120 during thesecond relationship between the body portion 120 and the tool 7, thefirst generally radial flow passage 142 b may feed into the axial flowpassage 142 a rather than the variable volume chamber 140, thus theprimary flow of flushing fluid bypasses the variable volume chamber 140,which is also reduced in capacity. The reduced capacity of the variableaxial volume chamber 140 enhances the ability to increase the fluidpressure for dislodging the slotting device 100, and by limitingflushing fluid communication between the variable volume chamber 140 andthe flow passage 142, the flushing fluid provides less damping wherebyimpact stress waves generated by the percussion device 4 may betransmitted to the slotting device 100 to assist in dislodging the guideportion 110 with respect to the previously drilled hole.

Thus, the third diameter portion 124 d and the second generally radialflow passage 142 c act like a valve to automatically control theposition of the sleeve 122 with respect to the tool 7, therebyautomatically reacting to feeding resistance of the guide portion 110.When the guide portion is jammed in the previously drilled hole, theflow through the slotting device is blocked and the fluid pressure isincreased. This can be monitored by means of one or more pressuresensor. Measuring results can be transmitted from the sensor to thecontrol unit 63 including a control strategy. When a predeterminedpressure limit is exceeded the control unit 63 may stop drilling andreverse the feed direction of the drilling machine.

Referring now to FIGS. 9-11, a second preferred embodiment of theslotting device 100 is described. The same reference numbers are used toindicate substantially identical features in both preferred embodiments,and no further explanation will be given.

Whereas the variable volume chamber 140 of the first preferredembodiment is in the shape of an annulus, with the tool 7 defining thepiston portion 7 a, the variable volume chamber 140 a according to thesecond preferred embodiment has a generally cylindrical shape with asleeve portion 122 and a dampening piston 128 disposed within a flowpassage 142 that extends through the tool 7. The flow passage 142includes at least one axial flow passage 142 a (four are shown in FIG.10), a first generally radial flow passage 142 b, and a second generallyradial flow passage 142 c. The first generally radial flow passage 142 bconnects a first portion of the flow passage 142 to a first axial end ofthe axial flow passage 142 a, and the second generally radial flowpassage 142 c connects a second axial end of the axial flow passage 142a to the second portion of the flow passage 142 through the tool 7.

The piston 128 includes an interior portion 128 a, an exterior portion128 b, and at least one coupling portion 128 c. The exterior portion 128b may comprise two halves the inner surfaces of which includeprotrusions for forming coupling portions 128 c, and wherein the halvesare arranged against each other and coupled with the interior portion128 a for example by screw joints. Each coupling portion 128 c defines aweb that extends between and fixes together the interior and exteriorportions 128 a, 128 b of the piston 128. The interior portion 128 adefines a first working pressure surface 80 affecting in drillingdirection D and a second working pressure surface 81 affecting inreverse direction R when pressure fluid is arranged to flow through theslotting device 100. During the first relationship, the same pressureaffects to the working pressure surfaces 80, 81 having the same surfacearea, whereby forces affecting the piston 128 are in equilibrium and thepiston is positioned in its middle position. The exterior portion 128 bslidingly receives the tool 7 and contiguously engages the sleeveportion 122 during the first relationship between the slotting device100 and the tool 7. There are axial gaps G in drilling direction D andin reverse direction R between the tool 7 and the damping piston 128 soas to prevent mechanical axial contact between them.

When the feeding resistance of the guide portion 110 increases thedampening piston 128 moves in reverse direction R in relation to thetool 7, as shown in FIG. 11. During the second relationship between theslotting device 100 and the tool 7, the flushing fluid flow through theaxial flow passage 142 a is restricted by virtue of the piston 128 atleast partially closing the first generally radial flow passage 142 b.Because of this, the fluid pressure affecting on the first workingpressure surface 80 increases and the fluid pressure affecting on thesecond working pressure surface 81 decreases, whereby a greater force isgenerated towards the drilling direction D. The piston 128 alsorestricts the fluid flow in case the piston 128 moves in drillingdirection D in relation to the tool 7. This situation may take placewhen drilling downwards. Thus, the dampening piston 128 automaticallyadjusts the feed force transmitted to the guide portion 110.

During the normal slot drilling the dampening piston 128 is not inmechanical axial contact with the tool 7. Forces affecting on thepressure working surfaces 80, 81 of the piston 128 ensure that no axialmechanical surfaces between the tool 7 and the piston 128 are againsteach other. The feed force is transmitted to the piston 128 by means ofthe fluid in the axial volume chamber 140 a. Thereby the transmission ofstress pulses to the slotting device is dampened.

Let it be mentioned that it is possible to conduct any other fluid thanflushing fluid to one or more axial volume chamber of the slottingdevice. The fluid can be for example hydraulic fluid led from the feedpump 12, the impact pump 13 or the rotation pump 14. In this embodimentthe tool 7 has to be provided with a special fluid channel and an axialvolume chamber separated from the flushing system.

FIG. 12 shows a hold device 64 having an opening 66 through which theslotting device 100 can be pushed. Dimensions and form of the opening 66is designed according to a cross sectional profile of the slottingdevice 100, whereby it includes two intersecting minor openings. Theopening 66 may be provided with a flexible sealing material 67 such asrubber and having several cuts 68 for facilitating the penetration.

It will be obvious to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The invention and its embodiments are not limited to the examplesdescribed above but may vary within the scope of the claims.

1. A rock drilling unit for slot drilling, comprising a feed beam, arock drilling machine arranged on the feed beam, and comprising apercussion device and a flushing device, a tool connected to the rockdrilling machine, and wherein the percussion device is arranged toproduce impact stress waves directed to the tool, and the flushingdevice is arranged to supply flushing fluid through the tool forflushing drilling waste from a hole being drilled, a feeding device,which is arranged to move the drilling machine on the feed beam and tofeed the tool in the hole being drilled, a slotting device connected tothe rock drilling machine and comprising a guide portion, a body portionand at least one strut extending between and coupling the guide portionand body portion, and wherein the guide portion is disposed in apreviously drilled hole, and wherein the tool is arranged slidinglythrough the body portion, and between the body portion of the slottingdevice and the tool there is at lest one axial volume chamber containingfluid so as to dampen transmission of the impact stress waves from thepercussion device to the slotting device.
 2. The rock drilling unitaccording to claim 1, wherein the axial volume chamber is connected tothe flushing device by means of at least one flow channel, and the axialvolume chamber contains flushing fluid.
 3. The rock drilling unitaccording to claim 1, wherein the slotting device is a dismountableauxiliary device connected to a shank of the rock drilling machine or toa drill rod connected to the shank.
 4. The rock drilling unit accordingto claim 1, wherein the body portion of the slotting device and the toolmutually define the at least one axial volume chamber containing fluid.5. The rock drilling unit according to claim 1, wherein the body portionof the slotting device and the tool mutually define the at least oneaxial volume chamber containing fluid, the body portion of the slottingdevice comprises a sleeve including a bore through which the toolextends, the bore of the sleeve comprises a first diameter portion, asecond diameter portion smaller than the first diameter portion, and ashoulder portion extending between and coupling the first diameterportion and second diameter portion, the first diameter portion of thebore slidingly receives a piston portion of the tool, and the seconddiameter portion of the bore receives a rod portion of the tool, theaxial volume chamber comprises an annulus that is defined radiallybetween the first diameter portion of the bore and the rod portion ofthe tool, and is defined axially between the piston portion of the tooland the shoulder portion of the bore, the slotting device furthercomprises a flow passage supplying the flushing fluid along the tool,the flow passage comprises an axial flow passage disposed radiallybetween the rod portion of the tool and the second diameter portion ofthe bore, a first generally radial flow passage connecting a firstinternal passageway of the tool to a first axial end of the axial flowpassage, and a second generally radial flow passage connecting a secondinternal passageway of the tool to a second axial end of the axial flowpassage, the bore of the sleeve comprises a third diameter portionsmaller than the second diameter portion, the third diameter portionslidingly receives the rod portion of the tool, and relative axialdisplacement of the tool with respect to the body portion restrictsfluid flow through the second generally radial flow passage andincreases fluid pressure moving the body portion with respect to thetool.
 6. The rock drilling unit according to claim 1, wherein betweenthe tool and the body portion there is a dampening piston, which is inaxial connection to the body portion and is in the axial directionseparated by means of fluid from the tool.
 7. The rock drilling unitaccording to claim claim 1, wherein between the tool and the bodyportion there is a dampening piston, which is in axial connection to thebody portion and is in the axial direction separated by means of fluidfrom the tool, the body portion of the slotting device comprises asleeve including a bore through which the tool extends, the toolcomprises a flow passage that extends through it, the dampening pistoncomprises an interior portion arranged within the flow passage, anexterior portion around the tool and at least one coupling portioncoupling the interior portion and exterior portion together, the pistonis arranged slidingly movably with respect to the tool, the interiorportion comprises a first working pressure surface affecting towards thedrilling direction and a second working pressure surface affectingtowards the reverse direction, a first axial volume chamber is on thefirst working pressure surface side of the piston and the fluid thereinis transmitting the feed force from the tool via the piston to thesleeve, and a second axial volume chamber is on the second workingpressure surface side of the piston and the fluid therein preventsmechanical axial contact between the tool and the piston in the drillingdirection.
 8. The rock drilling unit according to claim 1, whereinbetween the tool and the body portion there is a dampening piston, whichis in axial connection to the body portion and is in the axial directionseparated by means of fluid from the tool, the body portion of theslotting device comprises a sleeve including a bore through which thetool extends, the tool comprises a flow passage that extends through it,the dampening piston comprises an interior portion arranged within theflow passage, an exterior portion around the tool and at least onecoupling portion coupling the interior portion and exterior portiontogether, the piston is arranged slidingly movably with respect to thetool, the interior portion comprises a first working pressure surfaceaffecting towards the drilling direction and a second working pressuresurface affecting towards the reverse direction, a first axial volumechamber is on the first working pressure surface side of the piston andthe fluid therein is transmitting the feed force from the tool via thepiston to the sleeve, a second axial volume chamber is on the secondworking pressure surface side of the piston and the fluid thereinprevents mechanical axial contact between the tool and the piston in thedrilling direction, the flow passage of the tool comprises at least oneaxial flow passage, which connects the axial volume chambers, andwherein an axial movement of the piston relative to the tool in thereverse direction is arranged to restrict the pressure of the fluidaffecting the first working pressure surface thus increasing the feedforce transmitted via the piston to the sleeve.
 9. The rock drillingunit according to claim 1, wherein the guide portion comprises at leastone elongated guiding flange extending longitudinally along a peripheralsurface of the guide portion.
 10. The rock drilling unit according toclaim 1, wherein the feed beam is provided with a hold device at thedistal end of the feed beam, and the hold device comprises an opening,which is dimensioned according to a cross sectional profile of theslotting device allowing the slotting device to be pushed through thehold device.
 11. A slotting device comprising: an elongated toolincluding a first end and a second end, and wherein the first end isprovided with first coupling means for attaching the slotting device toa shank of a drilling machine or to a drill rod connected to the shank,and wherein the second end is provided with a drill bit, a body portionthrough which the tool is arranged, a guide portion disposable in apreviously drilled hole, and at least one strut extending between andcoupling the guide portion and body portion, and the slotting device isprovided with at least one axial volume chamber between the body portionand the tool, and wherein the slotting device comprises at least oneflow channel for directing fluid into the chamber, whereby the fluid inthe chamber is arranged to transmit axial forces from the tool to thebody portion.
 12. The slotting device according to claim 11, wherein theslotting device comprises at least one feed channel for feeding flushingfluid from the rock drilling machine into the axial volume chamber andat least one discharge channel for discharging flushing fluid from theaxial volume chamber to the hole being drilled, whereby flushing fluidis arranged to flow through the axial volume chamber.
 13. The slottingdevice according to claim 11, wherein the slotting device comprisesmeans for monitoring axial forces opposing the disposal of the guideportion into the previously drilled hole, and means for increasingpressure of the fluid affecting in drilling direction on at least oneworking pressure surface of the at least one axial volume chamber as aresponse to the monitored opposing forces, whereby axial forcetransmitted to the guide portion is increased.
 14. The slotting deviceaccording to claim 11, wherein the slotting device comprises valve meansfor affecting the volume flow through the axial volume chamber as aresponse to the relative axial position of the tool and the bodyportion.
 15. A method for slot drilling, comprising: drilling closelytogether a plurality of holes so as to form a slot in a rock material,using in drilling a rock drilling machine comprising a percussion devicefor generating percussion pulses to a tool connected to a rock drillingmachine, connecting a slotting device to the rock drilling machine, theslotting device comprising: a body portion through which the tool isarranged, a guide portion, and at least one strut extending between andcoupling the guide portion and body portion, disposing a guide portionin a previously drilled hole for maintaining the course of thepreviously drilled hole for the new hole being drilled, and transmittingduring drilling a feed force towards the drilling direction from thetool to the body portion of the slotting device and further to the guideportion, transmitting the feed force to the body portion of the slottingdevice in the drilling direction by means of fluid in at least one axialvolume chamber between the tool and the body portion, and dampeningtransmission of the impact stress waves from the percussion device tothe slotting device by means of the fluid in the at least one axialvolume chamber.
 16. A method as claimed in claim 15, comprisinginfluencing pressure of the fluid in the axial volume chamber inresponse to the axial movement between the body portion and the toolarranged to slide longitudinally relative to each other.
 17. A method asclaimed in claim 15, comprising influencing pressure of the fluid in theaxial volume chamber in response to the axial movement between the bodyportion and the tool arranged to slide longitudinally relative to eachother, arranging fluid flow through the axial volume chamber, andrestricting the fluid flow through the axial volume chamber when themovement of the guide portion in the previously drilled hole ishindered, whereby the feed force transmitted to the guide portion isincreased.
 18. A method as claimed in claim 15, comprising influencingpressure of the fluid in the axial volume chamber in response to theaxial movement between the body portion and the tool arranged to slidelongitudinally relative to each other, arranging fluid flow through theaxial volume chamber, restricting the fluid flow through the axialvolume chamber when the movement of the guide portion in the previouslydrilled hole is hindered, whereby the feed force transmitted to theguide portion is increased arranging fluid flow through the axial volumechamber, closing the discharge fluid flow through the axial volumechamber when the movement of the guide portion in the previously drilledhole is stopped, whereby the pressure of the fluid in the axial volumechamber increases, monitoring the pressure of the fluid affecting in theaxial volume chamber, and reversing the feed movement of the rockdrilling machine when the pressure of the fluid in the axial volumechamber exceeds a predetermined pressure limit.
 19. A method as claimedin claim 15, comprising connecting at least one drill rod to a shank ofthe drilling machine, and connecting the slotting device to a distal endof an outermost drill rod.
 20. A method as claimed in claim 15,comprising connecting the slotting device to a shank of the drillingmachine.
 21. A method as claimed in claim 15, comprising supporting theguide portion to surfaces of the previously drilled hole by means of atleast one elongated guiding flange extending longitudinally along aperipheral surface of the guide portion.
 22. A method as claimed inclaim 15, comprising conveying flushing fluid into the axial volumechamber.